An automobile having a large battery unit mounted therein, such as an electronic car, may have a floor structure including a pair of side sills extending in a fore-and-aft direction on either side of a vehicle body, a front floor panel extending between the side sills, a pair of floor frames (side members) extending in the fore-and-aft direction at positions spaced inward from the two side sills, respectively, in a lateral direction of the vehicle body, and a cross member extending in the lateral direction over the front floor panel (on the cabin side) and having ends attached to the two floor frames, respectively, wherein a battery unit is disposed flatly below the front floor panel between the two floor frames or on the inner side of the two floor frames in the lateral direction.
In the automobiles having such a battery unit arrangement, for the purpose of protecting the battery unit from damage in case of a side collision, an outrigger may be disposed between the side sill and the floor frame on each side of the vehicle body so that the outrigger collapses to absorb impact energy at the time of a side collision (see patent document 1, for example) or a reinforcement member (brace) may be attached to each floor frame to prevent inward tilting of the floor frame at the time of a side collision (see patent document 2, for example).
Further, in the portion where the front floor panel is provided, a cross member may be disposed so as to extend in the lateral direction of the vehicle body and be attached to the side sills or to the floor frames on either side of the vehicle body, such that the cross member transmits a side impact load from the floor frame on one side of the vehicle body to the floor frame on the other side (see patent documents 1, 2 and 3, for example).